Method of processing a material by means of a laser beam

ABSTRACT

A method of processing material with a laser beam. The material has two surfaces. The beam is focused by a multilens objective in a number of focal points which are approximately positioned on a common axis with an angle to the first surface. The focal points are spaced apart and used for cutting plates with several focal points being utilized for melting and cutting the plate material. As a result, a good cutting notch is obtained with good separation of the cut parts and poor adhesion of slag.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of processing a material with a firstand a second surface by means of a laser beam which for instance bymeans of a multilens objective is focused in a number of focal points,where said focal points are approximately positioned on a common axisforming an angle with the first surface and are spaced apart.

2. Discussion of the Background

German Auslegeschrift No. 2,713,904 discloses a way of processing anarticle by means of a laser beam, said laser beam being focused in twofocal points by means of a multilens objective. This processing methodis used for drilling holes, whereby one focused bundle of rays is usedfor a melting of the surface of the article and the second bundle ofrays presents a focal point positioned below the focal point of thefirst bundle of rays and is used for preheating the area surrounding thelocation of the article to be melted so as subsequently to be removed byway of evaporation. Such a processing method avoids to a certain degreeformation of burrs at the edge of the hole. The lower focal point is,however, not utilized.

A growing demand has applied within the material processing industryemploying lasers for a possibility of cutting in thick plates, such assteel plates of a thickness of 15 mm or more. As the cutting capacity ofthe laser beam is best on or adjacent the surface it is focused on,problems apply to transferring the effect to portions of the platepositioned below said surface. Moreover, the second surface of thematerial is encumbered with problems of an increased amount of adheringslags and a poor cutting quality, which inter alia results in a poorseparation of the cut parts and may necessitate a finishing processing.

SUMMARY OF THE INVENTION

The object of the invention is to provide a method of processingmaterial by means of a laser, which ensures an improved processingquality in connection with thick materials. Furthermore, the expenditureof protecting gases must be low.

A method of the above type is according to the invention used forcutting plates, whereby several focal points are utilized for meltingand cutting the plate material. The multilens objective has the effectthat the total bundle of rays is relatively narrow, whereby the nozzlefor protecting gases and consequently the expenditure of said protectinggases can be reduced correspondingly. It is well known that theprotecting gases are very important for the quality and the cut.

According to a preferred embodiment of the invention, the focal pointsare positioned at a fixed distance relative to one another and to thefirst and the second surface.

It is advantageous for the complexity of the focusing opticalinstruments when the number of focal points is two.

It is furthermore advantageous when the distance between the headcomprising the optical instruments and the first surface can beincreased in such a manner that the focal point adjacent the secondsurface during the cutting can be caused to be positioned on the firstsurface, the so-called starting holes thereby being provided in animproved manner. In addition, the risk of the optical instrument beingdamaged by metal sprayings has been reduced.

A further advantage is found in connection with ignition, melting andremoval of melt and slags by at least one of the focal points beingpositioned between the first and the second surface, adjacent the secondsurface or adjacent the first and the second surface, respectively,

In order to facilitate the penetration of the laser beam into thecutting notch it is furthermore advantageous when the focusing opticalinstruments focus the laser beam in several focal points, the distanceof which from the second surface is increased concurrently with anincreasing distance of the light from the central axis of the laser beamin such a manner that the central portion of the laser beam is focusedin the focal point adjacent the second surface.

BRIEF DESCRIPTION OF THE DRAWING

Two embodiments of the invention are described in greater detail belowwith reference to the accompanying drawing, in which

FIG. 1 a illustrates a laser cutting head with transmittent opticalinstruments,

FIG. 1 b illustrates a laser cutting head with reflecting opticalinstruments,

FIG. 2 a shows a transmittent optical instrument forming three focalpoints,

FIG. 2 b shows a reflecting optical instrument forming three focalpoints,

FIG. 3 a illustrates the cut ting head of FIG. 1 a at a distance fromthe surface, and

FIG. 3 b illustrates the cutting head of FIG. 1 b at a distance from thesurface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first made to FIG. 1 a, where a plate 6 to be cut by meansof a laser is shown. The plate comprises a first surface 8 and a secondsurface 9. A movable, integrated optics/nozzle system, also called acutting head 10, is provided above the first surface 8 of the plate 6.The cutting head 10 is movable in a plane parallel to the first surface8 of the material to be cut in, whereby optional shapes can be cut insaid material. The latter is known per se and is therefore not discussedin greater detail. Furthermore the cutting head 10 is movable to apredetermined degree perpendicular to the first surface 8 in such amanner that during the cutting it can enter an optimum distance relativeto a flow of cutting gas and the focusing of the laser beam 2.

The cutting head 10 comprises a pressure chamber 3 with an inlet opening4 allowing a continuous filling of cutting gases into said pressurechamber 3, as well as an outlet opening 5 directing the gas towards thecutting location. The gas used depends on the material to be cut, buttypically it is oxygen in connection with ordinary steel to be burntaway, or an inert gas, such as nitrogen, in connection with stainlesssteel being melt away.

In addition, the cutting head 10 comprises an optical instrument 1 a, 1b, 21 a, 21 b focusing a laser beam 2 in a number of focal points F₁,F₂, . . . , F_(n). These focal points are scattered on a common axis A,which forms an angle, typically a right angle with the first surface 8of the material to be cut. These focal points F₁, F₂, . . . , F_(n) areinterspaced a fixed distance relative to one another and relative to thefirst and the second surface 8, 9 of the material. For illustrativereasons, the FIGS. 1 a and 1 b are diagrammatic vies of a cutting notch7, in which the focal point F . . . is positioned.

In the embodiment shown in FIG. 1, the optical instrument 1 a, 1 b isformed such that the central portion of the instrument, i.e. within d₂,focuses the central portion of the laser beam 2 in the focal point F₂adjacent the second surface 9 of the material, whereas thecircumferential portion outside d₂ focuses the outer portion of saidlaser beam 2 in the focal point F₁ adjacent the first surface 8 of thematerial. In the illustrated embodiment, the focal point F₁ is placedabove the surface 8 in view of the cutting, but it is also possible toplace all the focal points F₁, F₂, . . . , F_(n) between the first andthe second surface 8, 9.

The optical instrument can be structured in many ways. The Figuresillustrate simple embodiments using a lens 1 a or a mirror 1 b.

The FIGS. 2 a and 2 b show embodiments of optical instruments 21 a, 21 bwith several focal points F₁, F₂, . . . , F_(n), only three beingillustrated for the sake of clarity. In this case, the focal points ofrespective concentric portions of the optical instrument 21 a, 21 b areformed such that the focal length decreases concurrently with anincreasing distance from the centre.

The distance between the entire cutting head 10 and the first surface isvariable in such a manner that during the starting procedure it can beincreased whereby the focal point F₂ ordinarily positioned adjacent thesecond surface 9 during the cutting can be caused to be positioned onthe first surface. The resistingly increased distance between thecutting head 10 and the first surface 8 reduces the risk of sprayings ofmelt material returning through the nozzle 5 so as to destroy theoptical instruments 1 a, 1 b, cf. FIGS. 3 a and 3 b where thediagrammatic cutting notch 7 has been maintained for illustrativereasons so as to provide an improved view of the beam passage, but saidnotch does not, of course, exist before the cutting has been initiated.

Although the embodiments include simple lens members, it is alsopossible to use more complicated arrangements, such as combinations oflenses which in combination form the desired number of focal points.

It is also possible to a certain degree to deviate from the exact axialpositioning of the focal points or the right angle of this axis with thesurface without deviating from the basic idea of the invention. Such aprocedure is for instance possible as long as it is advantageous for thecutting speed that the cutting in the deep layers is performed involvinga minimum displacement relative to the layers thereabove.

What is claimed is:
 1. A method of processing a plate material with afirst surface and a second surface by means of a laser beam, comprisingthe steps of: focusing the laser beam by means of a multilens objectiveat plural focal points, positioned approximately on a common axisforming an angle with the first surface and fixed spaced apart from oneanother; and using the focal points for melting and cutting the platematerial, including focusing a first focal point at a first distancealong said axis and a second focus point at second distance farther fromsaid multlens objective along said axis, starting cutting with saidsecond focal point positioned on the first surface, varying, after saidstarting cutting step, a location of said multilens objective relativeto said plate material so that said first focal point is positionedadjacent said first surface and said second focal point is positionedadjacent said second surface.
 2. The method of claim 1, using only saidfirst and second focal points for melting and cutting.
 3. The method ofclaim 1, comprising: focusing a central portion of the laser beam atsaid second focal point.
 4. The method of claim 1, wherein said focusingstep comprises: focusing the laser beam at plural focal points, suchthat after the step of starting and cutting the distance of the focalpoints from the second surface is increased concurrently with theincreasing distance of the light from the central axis of the laserbeam.
 5. A method of processing a plate material with a first surfaceand a second surface by means of a laser beam, comprising the steps of:focusing the laser beam by means of a multilens objective at pluralfocal points, positioned approximately on a common axis forming an anglewith the first surface and fixed spaced apart from one another; andusing the focal points for melting and cutting the plate material,including focusing a central portion of the laser beam in a first focalpoint, starting cutting with said first focal point positioned on thefirst surface, varying, after said starting cutting step, a location ofsaid multilens objective relative to said plate material so that saidfirst focal point is positioned adjacent said second surface and asecond focal point is positioned adjacent said first surface.
 6. Themethod of claim 5, wherein said focusing step comprises: focusing thelaser beam at plural focal points, such that after the step of startingand cutting the distance of the focal points from the second surface isincreased concurrently with the increasing distance of the light fromthe central axis of the laser beam.